Sensor devices based on magnetic transmitters and associated pick-ups which are used for detecting rotational movements, usually have a reference detection region, which can be used to generate a reference signal that provides a reference position marking during the detection of the rotational movement.
A reference detection region 213 of this type is illustrated in FIG. 5, in which an excerpt from a rotor provided from alternating first and second transmitter elements 101, 102 is shown. Transmitter elements of this type can be provided for example from permanent magnets which are arranged alternately with regard to their north-south direction, which is oriented parallel to the axis of rotation of the rotor. Thus, in FIG. 5, for example, the first transmitter elements 101 are formed as an N pole (north pole), while the second transmitter elements 102 are formed as an S pole (south pole).
The conventional arrangement shown in FIG. 5 has a reference detection region 213, which is characterized by the fact that three identical transmitter elements 102 arranged one behind another are formed. The introduction of such an asymmetry into the circumferential arrangement of the magnetic poles has significant effects on the magnetic flux to be detected by a pick-up unit (not shown). The magnetic fluxes detected by means of the conventional rotor and the reference detection region 213 described are illustrated in FIGS. 6(a) and (b) and FIGS. 7(a) and (b). In this case, the individual curve profiles correspond to specific magnetic fluxes calculated or simulated for different air gaps. Consequently, a first air gap 201 is larger than a second air gap 202, which is in turn larger than a third air gap 203, which is in turn larger than a fourth air gap 204. In this case, the size of the air gap denotes a distance between the pick-up unit and the first and second transmitter elements 101 and 102 moving past the latter. In the example shown in FIGS. 6 and 7, the first air gap 201 has a value of 1 mm, the second air gap 202 has a value of 2 mm, the third air gap 203 has a value of 3 mm, and the fourth air gap 204 has a value of 4 mm.
FIGS. 6(a), (b) to 7(a), (b) show magnetic flux profiles as a function of a detection position 210, wherein the detection position has the reference detection region 213 in the middle of the horizontal axis (x-axis). Consequently, it can be discerned from FIGS. 6 and 7 that, in the middle of the x-axis, an alteration of the magnetic flux occurs, in such a way that this alteration can be used as the reference position. To the left and right of this altered region of the magnetic flux, the magnetic flux has a regular region given by the alternating arrangement of the first and second transmitter elements on the rotor.
The first and second transmitter elements 101, 102 are illustrated for reference in the lower part of FIG. 6(a). The alteration of the magnetic flux 209 in the reference detection region 213 should be pointed out, in particular, said region comprising second transmitter elements 102r arranged one behind another, not alternately, in the conventional example shown.
FIG. 6(b) shows the magnetic flux profile illustrated in FIG. 6(a) in a differential form, that is to say that the profile shown in FIG. 6(b) corresponds to the differentiated magnetic flux profile 209. Consequently, FIG. 6(a) illustrates a tangential magnetic flux 209, while FIG. 6(b) illustrates a differential tangential magnetic flux profile 209′.
Furthermore, FIG. 7(a) shows a normalized tangential magnetic flux 214, wherein a normalization is normalized with regard to each individual profile corresponding to the first to fourth air gaps 201-204.
FIG. 7(b) illustrates the differentiated normalized tangential magnetic flux profile of FIG. 7(a), that is to say a differential normalized tangential magnetic flux 214′.
Since the profile illustrated in FIG. 7(b) is always detected by means of the pick-up unit, a problem in the generation of a reference position signal by means of the conventional rotor arrangement shown in FIG. 5 is clear. The possibility of detecting the reference position varies greatly with the air gap, as can be discerned from the curve profiles for the first to fourth air gaps 201-204. Only the regions of the third and fourth air gaps 203, 204 have an approximately matching profile in the reference detection region, but not in the other regions.
Consequently, it is a significant disadvantage of the conventional magnetic sensor device described that the near field in the vicinity of the reference point is highly influenced on account of the irregular arrangement of the first and second magnetization elements. Furthermore, this magnetic field disadvantageously varies greatly with the distance between pick-up unit and transmitter unit, that is to say significantly with the size of the air gap 201, 202, 203 and 204.
Both factors disadvantageously impair the operating behavior of conventional magnetic sensor devices, wherein manufacturing tolerances such as, for example, the design of the air gap or the distance between transmitter unit and pick-up unit and the like have a major disadvantageous influence.